Cardiac rhythm management devices are implantable devices that provide electrical stimulation to selected chambers of the heart in order to treat disorders of cardiac rhythm. A pacemaker, for example, is a cardiac rhythm management device that paces the heart with timed pacing pulses. The most common condition for which pacemakers have been used is in the treatment of bradycardia, where the ventricular rate is too slow. If functioning properly, the pacemaker makes up for the heart's inability to pace itself at an appropriate rhythm in order to meet metabolic demand by enforcing a minimum heart rate and/or artificially restoring AV conduction. Implantable devices may also be configured to treat tachyarrhythmias such as fibrillation with electrical stimulation.
As a part of performing their functions in delivering therapy, implantable cardiac devices may equipped with various sensing modalities for detecting cardiac electrical activity as well as measuring other physiological parameters. Other types of implantable medical devices (such as monitoring-only devices or devices for delivering other types of therapy) may also have cardiac or non-cardiac sensing capabilities for acquiring physiological data. The data collected by an implantable medical device can be transmitted over a wireless telemetry link to an external programmer or other external device when the implantable device is interrogated.